Diffractive optical element
Described herein are embodiments of a diffractive optical element ( 23 ) such as a grism. In one embodiment, the diffractive optical element ( 23 ) includes an input surface ( 31 ) configured to receive an input optical signal ( 29 ), a diffractive surface ( 33 ) adapted to spatially disperse the input optical beam ( 29 ) into a dispersed signal and an output surface ( 35 ) configured to output the dispersed signal from the diffractive optical element. The input surface ( 31 ) and the diffractive surface ( 33 ) are non-parallel and the diffractive surface ( 33 ) is formed in situ by a photolithographic technique.
1 . A diffractive optical element including:
a prism;
an input surface of the prism configured to receive an input optical beam;
a diffractive surface of the prism adapted to spatially disperse the input optical beam into a dispersed signal;
an output surface of the prism configured to output the dispersed signal;
wherein the output surface and the diffractive surface are non-parallel; and
wherein the diffractive surface is formed on a surface of the prism.
2 . The diffractive optical element according to claim 1 wherein the diffractive surface and input surface are non-parallel.
3 . The diffractive optical element according to claim 1 wherein the input surface is the output surface.
4 . The diffractive optical element according to claim 1 wherein the optical element is a triangular prism.
5 . The diffractive optical element according to claim 1 wherein the optical element is a trapezoid.
6 . The diffractive optical element according to claim 1 wherein the diffractive surface is formed by:
depositing a pattern material layer of pattern material on the diffractive surface;
applying a photoresist layer to the pattern material layer;
creating a diffractive pattern in the photoresist layer using a light source; and transferring the diffractive pattern in the photoresist layer to the pattern material.
7 . The diffractive optical element according to claim 1 wherein the diffractive surface is formed by:
depositing a photoresist layer on the diffractive surface; and
creating a diffractive pattern in the photoresist layer using a light source.
8 . The diffractive optical element according to claim 6 wherein the pattern material is selected from one or more of Si3N4, TiO2, HfO2, amorphous silicon, high refractive index polymer, reflective metal and Ta2O5.
9 . The diffractive optical element according to claim 8 wherein the high refractive index polymer is spin-on-glass or photoresist.
10 . The diffractive optical element according to claim 8 wherein the reflective metal is selected from chromium, gold, silver, aluminum or nickel.
11 . The diffractive optical element according to claim 6 wherein the diffractive pattern in the photoresist layer is created by illuminating the photoresist layer through a photo mask while moving the photoresist layer substantially perpendicular relative to the mask.
12 . The diffractive optical element according to claim 11 wherein the photoresist layer includes an anti-reflective coating and primer.
13 . The diffractive optical element according to claim 6 wherein the diffractive pattern in the photoresist layer is created by illuminating the photoresist layer through a photomask.
14 . The diffractive optical element according to claim 11 wherein the movement is substantially continuous.
15 . The diffractive optical element according to claim 11 wherein the photoresist layer is moved a distance of
Z
T
=
2
p
2
λ
where p is the spatial period of the mask and λ is the wavelength of the light source.
16 . The diffractive optical element according to claim 14 wherein the photoresist layer is moved a distance of
Z
T
=
2
p
2
λ
where p is the spatial period of the mask and λ is the wavelength of the light source.
17 . The diffractive optical element according to claim 1 configured to operate in a wavelength selective switch.
18 . The diffractive optical element according to claim 17 wherein the input optical signal includes a plurality of optical wavelength channels.
19 . The diffractive optical element according to claim 1 wherein the element includes a lens.
20 . The diffractive optical element according to claim 1 wherein the input surface is the diffractive surface.
21 . The diffractive optical element according to claim 1 ,
wherein
the input surface and the diffractive surface are separated by a distance of greater than 5 mm.
22 . The diffractive optical element according to claim 21 wherein the element is anon-wafer structure.
23 . The diffractive optical element of claim 1 , wherein the diffractive surface is formed in a same prism material as the input surface and the output surface.
24 . A method of forming diffractive optical element including:
depositing a pattern material layer of pattern material directly onto a first surface a monolithic prism, the monolithic prism having;
an input surface configured to receive an input optical signal and
an output surface configured to output a dispersed signal,
wherein the input surface and the first surface are non-parallel;
applying a photoresist layer to the pattern material layer;
creating a diffractive pattern in the photoresist layer by illuminating the photoresist layer through a photo mask;
transferring the diffractive pattern in the photoresist layer to the pattern material layer to define a diffractive surface on the first surface, and
wherein the diffractive surface is formed in situ on the first a surface of the monolithic prism.
25 . The method of claim 24 , wherein the diffractive surface is formed in situ in the same monolithic prism as the input surface and the output surface.
26 . The method of claim 24 , wherein the diffractive optical element is a triangular prism, a trapezoid, or a non-wafer structure.
27 . The method of claim 24 , wherein the pattern material is selected from one or more of Si 3 N 4 , TiO 2 , HfO 2 , amorphous silicon, high refractive index polymer, spin-on-glass, photoresist, reflective metal, chromium, gold, silver, aluminum, nickel, and Ta 2 O 5 .
28 . The method of claim 24 , wherein the photoresist layer includes an anti-reflective coating and primer.
29 . The method of claim 24 , further comprising moving the diffractive pattern relative to a light source during the illumination.
30 . The method of claim 24 , further comprising adding the diffractive optical element to a wavelength selective switch.
31 . The method of claim 30 , wherein the movement is a distance of
z
T
=
2
p
2
λ
where p is a spatial period of the photo mask and λ is a wavelength of the illumination.